For specific mercenaries character strategies, you can try these but they arent necessarily the best way to use the character.
1.
: get rid of pistol+ammo, shotty everyone in the face, grenade minibosses
2.
: get rid of pistol, shotty everyone in the face. Use rocket launchers on first two minibosses, then shotty/melee the last one or use any found grenades.
3.
:go around shooting majini in the knees and melee kill them with your ak. save magnum and grenade launchers for bosses, but youll likely have to use some of their ammo on majini too if you arent being conservative and melee killing since ammo wil be split between three guns , although magnum ammo is rarer.
4.
: probably get rid of the pistol since youll want to get rifle and machinegun ammo more often. just hit majini almost anywhere with the rifle, im pretty sure every sniper rifle will one shot regular majini. be conservative with the mg if you can, but one basic mg strategy is to unload the clip on a majini when your combo is gonna run out
5.
: I havent played much with this character, but I'd probably get rid of the mg after using its ammo and just use the shotty. the mg clip is way too small in my opinion, so you'd probably prefer to get shotty and nade ammo. Use the grenade launcher when you need a lot of crowd control or for bosses.
6.
: first of all, get used to the bow. It one shots all majini unless they go parasite, then youll need two shots more to kill the parasite which is not long at all. Very easy to add to combos with that bow. Dont forget you have grenades, use them sparingly since youll almost always have more than enough space in your inventory. The nade launcher is nice since it comes with ice rounds, especially on the ship level. When facing a chainsaw guy, you can stand tall usually, because just about two shots will stun him with the bow. two shots will end his berserk form too, so aim well and he'll be no problem. You can also stun the chainsaw guys with the ice rounds but they wont freeze him obviously. executioners are tough to face in the prison in my experience, because once you get good with the bow, you tend to think youll always stun an enemy with it, if not kill it completely. yet, the executioners can usually get that axe down on you and you never know why.
7.
: ground attacks are great, youll easily get great scores just running around ground meleeing enemies. I wouldnt be surprised if leaderboards get reset and this move gets significantly reduced damage. the pistol gets headshots very easily, so it is hard to recommend you throw it away for more mg ammo. you get 5 flash grenades too, so this is a great character to use when you're gonna face parasites or the shell guys. (it might have sounded obvious but ive seen a lot of people not use flash grenades in those situations.
8.
: much better than the other version, you get a rifle instead of a pistol but no flash grenades. the rifle is a great way to keep a combo going, and dont forget to use the ground attack whenever possible.
9.
: pistol and handcannon and proximity mines, oh so fun. great to use in the mines level for dealing with reapers, although spending the time to put the proximity mines down will possibly end a combo for you. save the magnum ammo for bosses, probably only use this character if you are great with a pistol. if you're in a tough bind or you see a long line of enemies in a row, like the ancient ruins, press in on the right stick and you can dash through all the enemies. Watch out though because this takes away some health as a result.
10.
: pistol, magnum, and shotty, but no additional perks. You can either get rid of the pistol to get a better selection of ammo, or save the pistol since it will stun all enemies except maybe the reapers. very good character for using to get used to all the levels since its nice to choose what ammo you want to come from random drops. you also have the dash too so keep that in mind.
I would really appreciate any criticisms or additions to what I wrote here, these are just the basic things that come to my mind and my strategies are surely FAR from the most efficient way to use the characters.